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Re: DCT (forwarded)
On Mon, 1 May 1995, Mike Orton wrote:
> Date: Mon, 1 May 1995 23:21:46 -0700
> From: Mike Orton <orton at earthlink.net>
> To: Rob Lingelbach <rob at xyzoom.alegria.com>, telecine at xyzoom.alegria.com
> Cc: rich at pi.mte.com
> Subject: Re: DCT (forwarded)
> At 5:57 PM 4/30/95, Rob Lingelbach wrote:
> >--- Forwarded mail from "Richard Torpey" <rich at pi.mte.com>
> >From: "Richard Torpey" <rich at pi.mte.com>
> Rich, I have to tell you that we have yet to see any difference, or *measure* any difference between input and output on our DCTs, whether used for telecine, graphics or whatever.
> The principle relies upon the amount of correlation in a picture: every picture that Ampex came across, that was not a specially designed "break-it" test pattern, (i.e. any picture which conveys meaningful picture content), has greater than about 2.5:1 correlation in the transform domain where the compression acually occurs.
> This means that only *truly* redundant information is thrown away, leaving picture material untouched. That's not virtually untouched, but completely untouched. The reason it works is that we are dealing with real-world pictures. Even computer programs can be compressed *without loss* by a ratio of over 3:1. The "Stuffit" program on my Mac regularly achieves this ratio, and yet I can still run the decompressed applications fine. Try running "Stuffit" on a "Pict" file and see the compression ratio that can be achieved without trying.
> The result is that we dont have to feel "lucky". We can (and do) guarantee total transparency with all *legal* D-1 program material. The only downside to the whole process is that we cannot allow any errors to creep in at all. One error will corrupt an entire 8x8 block for a field, and be embarrasingly visible. Ampex, to their credit, have turned a vice into a virtue: they simply had to include an incredibly powerful error-correction mechanism in the DCT specification, to get around this potential mega-error problem. As it happens, this makes DCT actually *cleaner* than most D-1s which are error-concealed, not corrected.
> There, I told you Mike Arbuthnot had done a number on me, and really, that Swiss bank account number he slipped into my pocket helped a great deal too :-)
> P.S. anyone out there care to dispute the above? Havent had a good argument in ages.........
Can't dispute what I agree with. My experience with DCT while at VTA was
a good one, after some early software changes. (Wish I could say the
same for Digital Betacam, which seems to be becoming the format of choice
these days - unfortunately, to me.) The DCT's dual-standard capability is
a very useful convention, not only for telecine, but also for dual-standard
component edit suites. Besides, I'd sell more of my Reference Link
boxes if the world went DCT :-)